EP1484165A2 - Method for monitoring the manufacture of a fibre reinforced moulded part - Google Patents

Abstract

The component (34) is produced by introducing liquid resin into a fiber preform in a tool using a known method, e.g. vacuum injection. During the impregnation stage the resin flow front moves through the preform and the resulting test piece is excited with modulated heat waves (36). A response signal from the test piece is recorded for analysis (48). Heat waves (36) are directed towards a resin distribution fabric forming part of the preform. The response signal can be determined in either reflection or transmission modes and is recorded by a camera (40). Heat wave intensity is modulated during the test period. A resin front flow rate through the preform is determined by analysis of the phase signature and amplitude signature. One or both signatures can be determined by a Fourier transformation. For detecting air inclusions and similar faults a low amplitude, typically not > 1Hz., preferably not > 0.5Hz., but not less than 0.0001. Temperature varies during the measurement period. Test pieces (34) comprise a number of fiber preform layers including a resin distribution fabric. A specific calibration test piece of similar construction to a test piece can be used to determine an optimum frequency or frequency range for the modulation. Higher frequencies are used to test areas close to the surface and lower frequencies to test deeper areas. A determined flow rate of the resin front can be used to automate the component manufacturing process.

Description

The invention relates to a method for monitoring the production of a Component made of a fiber-reinforced material.

For example, EP 1 136 238 A2 describes a method for producing a Known component made of a fiber-reinforced material, in which one Semi-finished fiber material is supplied with liquid resin by applying negative pressure becomes. Such a process is also referred to as a vacuum injection process. Methods are also known in which the resin impregnation or resin infiltration of the fiber fabric of the semi-finished fiber product without applying negative pressure takes place.

The invention has for its object a method for monitoring the To provide manufacture of a component from a fiber-reinforced material.

This task is performed in the method mentioned at the beginning, the component is produced by infiltration of a semi-finished fiber product with liquid resin, solved according to the invention in that during the infiltration process DUT is thermally excited with modulated heat waves and that Response signal is registered.

The method according to the invention becomes a photothermal measuring method provided to monitor the infiltration process. Through the modulated heat waves, the test object is thermally excited and via the Response signal can be obtained statements about the test object. It has showed that this method is suitable for a resin fronts course during to determine the transient, variable process of resin infiltration.

Air inclusions can be determined, for example, by determining the resin front profile determine the quality of a finished component could result. The monitoring can be carried out non-destructively. Air can also enter the test specimen after resin infiltration has ended observe in the thermographic image.

Basically, it is also possible to carry out chemical reactions of the resin system (the matrix) to determine the resin fronts and thus information to determine the degree of crosslinking in the component.

According to the invention, a method is provided with which depth is resolved and the non-destructive development of the resin fronts in their temporal development lets track. This depth resolution becomes inhomogeneous transient system with changing physical and chemical Properties achieved.

The method according to the invention enables quality assurance with regard to perform the manufactured components, taking this quality assurance is accompanying the manufacturing process. The method according to the invention can be perform in a simple and inexpensive way. In particular, it can be used in a multilayer structure of an arrangement for producing the corresponding component. For example, the device under test can also be Monitor the vacuum film under which the test specimen for resin impregnation is arranged.

The method according to the invention can also be used, for example Examine areas near the surface in a targeted manner by using appropriately large areas Frequencies can be selected. This can be used, for example, for leaks recognize in a distribution medium such as a distribution fabric and this allows, for example, the ingress of air. Leave as well recognize outgassing. This in turn allows monitoring optimize in order to be able to produce a high quality component.

It is also possible to monitor the speed of a resin front during to determine the manufacture. This can, for example, from the phase signature and / or amplitude signature of the response signal can be determined. about The determined course of the speed can be infiltrated with resin monitor better. It is also possible to manufacture the component automate. For example, the speed curve of the Harzfront infiltration times can be calculated or estimated. Thereby again the end of infiltration can be determined. For example, then the resin supply is automatically switched off knowing the infiltration time become.

In particular, the test object is exposed to heat waves across the surface, in order to thermally excite the test object over a large surface area. This gives a response signal from which a resin fronts run based on an image plane can be determined, the corresponding one covers a large area. The device under test can also be volumetric thermal be excited, for example via microwaves or induction heating.

It can be provided that the response signal is determined in reflection. It is alternatively or additionally possible that the response signal in transmission is determined.

It is particularly advantageous if the test specimen is in the direction of a distributor fabric is exposed to heat waves. The distribution fabric is responsible for the resin supply to the fiber fabrics of the semi-finished fiber product. The distribution fabric thus determines the resin supply to the semi-finished fiber. The distribution fabric is then responsible for the training of resin fronts. By loading the distribution fabric with The laminate layers can be exposed to photothermal radiation accordingly thermally stimulate below the distributor fabric and in turn can be the course of the resin fronts, which is caused by the distribution fabric, determine. Air inclusions and the like can then be determined from this.

It is particularly advantageous if the response signal by a camera is registered. The response signal of the test object can be transmitted via the camera take up a large surface, which means that signals are generated at the same time registered over a large area. The camera is especially an infrared camera, which has a thermographic response signal of the examinee registered.

In particular, the test object is optically irradiated with appropriate lamps, which are intensity modulated or pulse modulated.

It is particularly advantageous if the heat waves are intensity-modulated are. Then the temperature modulation at all points of the test object, which are excited by the modulated heat waves are tracked across the surface become. The amplitude and phase can be determined at each pixel using an evaluation device determine, for example by pixel-wise Fourier analysis. Such a procedure is also called phase sensitive modulation thermography or Lockin thermography. According to the phase-sensitive modulation thermography for monitoring resin impregnation processes used.

Favorably, a speed profile becomes a progressive resin front determined in the phase signature and the amplitude signature. For example a phase image and an amplitude image are determined. From that then for air pockets and the like, which are expressed in the speed profile, be closed and in turn process quality assurance be performed.

It is particularly advantageous if a phase signature evaluation is carried out and, alternatively or additionally, an amplitude signature evaluation is carried out. This allows you to run a resin fronts determine in particular with regard to the corresponding speed profile and from this in turn, statements about air pockets and the like can be obtained. The evaluation via the phase signature has the advantage that a greater depth range can be achieved because the phase (other than the amplitude) largely independent of lighting inhomogeneities and surface defects of the examinee. Comparative measurements have shown that with a Phase signature evaluation an approximately twice greater depth range than with an amplitude signature evaluation can be achieved.

The amplitude signature and / or phase signature is preferably about Fourier transform determined.

It has been shown that for monitoring resin impregnation a deep Frequency range with frequencies below 1 Hz and especially below 0.5 Hz must be selected. The frequencies mentioned have been meaningful Amplitude images and phase images result in air pockets and the like can be determined.

It has also proven to be advantageous if the frequency is greater than Is 0.0001 Hz and in particular is greater than 0.001 Hz.

In particular, a non-stationary temperature state is measured, the it means that there is no waiting until a steady temperature occurs, since the processes themselves are non-stationary in resin impregnation are.

The method according to the invention can be used if the test object has a Has layer structure with fiber semifinished layers.

In particular, the layer structure has a distribution fabric for the resin, which is arranged on the semi-finished fiber. Such a layer structure is responsible for the formation of a wedge-shaped resin front, which in the unfavorable Case can lead to air pockets that negatively affect quality of a manufactured component.

The inventive method can also be used if such Distribution tissue is present and in particular can be speed profiles determine the resin front caused by the distribution fabric are.

It is favorable if a defined calibration test specimen is manufactured and on this a suitable frequency or a suitable frequency range for the modulation is determined. The optimized frequency or the optimized frequency range for monitoring resin infiltration in one UUT depends on the UUT itself. If a defined calibration test item is produced, which basically has the same structure as the DUT has (especially with regard to the semi-finished fiber) and one basically the same resin infiltration is carried out as for the one to be manufactured Component, then the optimized one can be used on this calibration test specimen Frequency can be determined. For example, in the calibration device under test targeted faults such as film strips installed on a bottom. The Frequency is chosen so that the disturbances can be recognized. With that certain frequency can then produce an actual component be monitored.

It can be provided that the frequency of the modulation is varied. This allows a component to have at least two frequencies, for example to be examined, for example, a near-surface area and to be able to examine a depth range.

For example, a higher frequency is used to check the surface Areas and a lower frequency are used to check deeper areas. When examining near-surface areas, for example Detect leaks in a manifold; it can be Detect air ingress or outgassing can be detected. about a deep investigation can determine the course of the resin front.

It is particularly advantageous if the speed curve is one Resin front is determined. The speed curve can be derived from the phase signature and / or determine the amplitude signature of the response signal. about disturbances in resin infiltration can be seen from the speed curve. It is also possible to use a known speed curve Calculate or estimate infiltration times. this makes possible automation of component production, for example because of the calculated or estimated infiltration time result the resin supply automatically can be stopped.

The inventive method can also be used if a Vacuum film is provided because the thermal excitation also through the Vacuum film can take place.

Figur 1

eine schematische seitliche Schnittansicht einer Anordnung zur Herstellung eines Bauteils aus einem faserverstärkten Werkstoff mittels Harzimprägnierung;

Figur 2

eine schematische Ansicht einer Meßanordnung zur Überwachung des Harzverlaufs bei dem Prüfling gemäß Figur 1;

Figuren 3(a), 3(b)

ein aufgezeichnetes Phasenbild für einen Beispielprüfling zu verschiedenen Zeiten;

Figur 3(c)

den Phasenverlauf längs der Linie X gemäß Figur 3 (b);

Figuren 4(a), (b)

Amplitudenbilder, welche für den gleichen Prüfling ermittelt wurden;

Figur 4(c)

den Amplitudenverlauf längs X gemäß Figur 4(b), und

Figur 5

die Tiefenreichweite in Abhängigkeit der Frequenz in doppeltlogarithmischer Darstellung an einem speziell präparierten Prüfling, wobei die obere Kurve durch Auswertung der Phasensignatur erhalten wurde und die untere Kurve durch Auswertung der Amplitudensignatur.

The following description of preferred embodiments serves in conjunction with the drawing to explain the invention in more detail.
Show it:

Figure 1

is a schematic side sectional view of an arrangement for producing a component from a fiber-reinforced material by means of resin impregnation;

Figure 2

a schematic view of a measuring arrangement for monitoring the resin flow in the test specimen according to Figure 1;

Figures 3 (a), 3 (b)

a recorded phase image for a sample under test at different times;

Figure 3 (c)

the phase curve along the line X of Figure 3 (b);

Figures 4 (a), (b)

Amplitude images which were determined for the same test object;

Figure 4 (c)

the amplitude curve along X according to Figure 4 (b), and

Figure 5

the depth range as a function of frequency in a double logarithmic representation on a specially prepared test specimen, the upper curve being obtained by evaluating the phase signature and the lower curve by evaluating the amplitude signature.

An example of a manufacturing arrangement, indicated generally at 10 A component made of a fiber-reinforced material is shown in FIG. 1. A corresponding arrangement and a method and an apparatus for manufacturing a workpiece made of a fiber-reinforced material using resin impregnation are described in EP 1 136 238 A2, to which hereby expressly Reference is made.

A semifinished fiber product 12, which has a plurality of laminate layers 14 (Laid fiber) is arranged on a mold 16. To the outside the semi-finished fiber 12 covered by a vacuum film 18.

A distribution fabric 20 is arranged above the semi-finished fiber 12, which covers the semi-finished fiber 12. About the distribution fabric 20 is the Semi-finished fiber 12 liquid resin for resin impregnation of semi-finished fiber 12 fed.

It can also be provided that between the distribution fabric 20 and the semi-finished fiber 12 is a release film 22 is arranged, which serves that after completion, the distributor fabric 20 more easily detached from the component can be and the component is made with a smoother surface.

A vacuum space 24 is formed by the vacuum film 18, in which the impregnating semi-finished fiber 12 is positioned. Compared to the 16 form this vacuum space 24 sealed by a seal 26.

The vacuum space 24 can be subjected to negative pressure in order to infiltrate the resin to promote the semi-finished fiber 12. To do this, flows into the vacuum space 24 a suction port 28 of a pump (not shown in the drawing) via the the vacuum can be generated in the vacuum space 24.

A feed connection 30 for liquid resin opens into the vacuum space 24, via which 20 resin can be supplied to the distributor fabric, which in turn is then from infiltrates the distribution fabric 20 from the semi-finished fiber 12.

In the so-called VARI process (vacuum assisted resin infusion process) is the semi-finished fiber 12 by means of negative pressure Liquid resin supplied, using a thermosetting resin as the resin is and the vacuum pressure is controlled and / or regulated be that based on the liquid resin, the boiling point curve of the resin is not exceeded. This process is described in EP 1 136 238 A2, to which express reference is made.

A resin front 32, which is wedge-shaped, forms during resin infiltration Has course. This formation of the resin front is due to the fact that the liquid resin is injected via the feed connection 30 and the Penetration of the resin into the semi-finished fiber 12 does not occur simultaneously over the entire Surface of the semi-finished fiber 12 takes place.

There is a fundamental problem that due to the resin front formation Air pockets can form during resin impregnation, which can affect the stability of the finished component.

According to the invention, a method is provided with which the production can be carried out of the component can be monitored by determining the resin front profile becomes.

For this purpose, as indicated in FIG. 2, a test specimen 34 with modulated heat waves is used 36 acted upon. The heat waves 36 are from a lighting device 38 delivered. The device under test 34 is thereby thermally excited and an infrared camera 40 registers the corresponding response signal of the test object 34th

The lighting device 38 is designed such that a surface 42 of the test specimen can be exposed to radiation over a large area. The infrared camera 40 registers a response signal of the entire surface 42. With the infrared camera 40 is in particular a high-resolution camera.

The response signal can be measured in reflection, and then the lighting device 38 and the camera 40 on the same page with respect the surface 42 are arranged.

It can also be provided that the device under test 34 is measured in transmission becomes. An illumination device 44 is then provided, which of the test specimen 34 is arranged on the other side like the camera 40.

In the example shown in FIG. 2, the lighting device then irradiates 44 a surface 46 of the test specimen 34 which lies opposite the surface 42.

It is also possible to measure reflection and transmission at the same time becomes. For thicker components, measurements are preferably made in reflection.

The heat waves 36 are in particular amplitude modulated, that is to say that Surface 42 or 46 is exposed to intensity-modulated radiation. It has proven beneficial if the frequency is in the range between 0.5 Hz and 0.001 Hz. There have been processes in this frequency range for the main infiltration in the manufacture of a component from one Have fiber-reinforced material observed. Experience shows that for Glass fiber reinforced semi-finished fiber products due to the poorer thermal conductivity the frequencies should be chosen rather lower.

An evaluation device 48 is provided, which is connected to the lighting device 38 (and possibly 44) is coupled and also to the Infrared camera 40 is coupled so that the excitation signals and response signals can be related to each other. The infrared camera 40 records the photothermal response of the device under test 34 to the Heat wave excitation.

By means of the evaluation device 48, the local is carried out pixel by pixel, the phase signature and / or the amplitude signature determined. For example, the amplitude image and the phase image determined from the response signal. The infrared camera 40 provides the corresponding ones Thermographic data to the evaluation device 48 for this evaluation to be able to perform. Such a procedure is also called phase sensitive Modulation thermography or Lockin thermography.

An easy evaluation is obtained when the modulated heat waves are sinus modulated. However, it is also possible in principle for this to be pulse-modulated or are otherwise modulated.

By means of the method according to the invention, transient changes become Processes observed in DUT 34. Accordingly, for the measurement also not waited until steady-state conditions arise.

The depth-resolved speed profile of the resin front 32 in the test specimen becomes 34 determined in the phase image and amplitude image. This is in conflict on the well-known use of Lockin thermography for materials with stationary Conditions where the change in thermal diffusivity is determined.

The frequency and the number of measuring cycles in the invention Process the speed of the advancing resin front 32 in one image plane. For example, peak distances (FIGS. 3 and 4) determined in the phase image and / or amplitude image.

Examples of phase images are shown in FIGS. 3 (a) and (b). Examples for amplitude images are shown in Figures 4 (a) and (b). This are the result of several measuring cycles as an integration over these measuring cycles.

These phase images and amplitude images were taken in a reflection measurement obtained, the test specimen 34 in an arrangement as shown in Figure 1 was exposed to radiation in one direction 50. So that corresponds a surface 52 of the assembly 10 which is to the surface of the Distribution fabric 20 is congruent, the surface 42 in the schematic Arrangement according to FIG. 2.

The image plane 54 is perpendicular to the direction 50. A resin infiltration direction 56 lies parallel to the image plane 54.

Resin fronts are clearly visible in FIGS. 3 (a) and 4 (a). This were represented by the markings drawn in the figures lifted.

Figures 3 (b) and 4 (b) show the further progress of the resin fronts. Figures 3 (b) and 4 (b) represent one compared to Figures 3 (a) and 4 (a) Shown at a later point in time. The figures show the wedge-shaped resin fronts, as shown schematically in Figure 1 is.

Figure 3 (c) shows the phase curve along the line X for the phase image of the Figure 3 (b). In area 58 you can see the course of the resin fronts.

The same applies to FIG. 4 (c), which shows the amplitude along the direction X for shows the amplitude image of Figure 4 (b). Here you can see in the with the Area 58 spatially coinciding area 60 the resin fronts.

Air inclusions in the test specimen 34 can lead to a deteriorated component quality to lead. Such air pockets can be seen in the amplitude image and in the phase image. This enables non-destructive detection during the manufacture of the component whether the properties of the infiltrated semi-finished fiber product 12 change during manufacture and thus in turn can be recognized - and non-destructively - whether a component with possibly reduced Quality was created due to air pockets.

It is also possible to chemical reactions of the resin system (the matrix) recognize which influence the resin fronts. That’s basically it possible to make statements about the degree of crosslinking of the component To obtain measurements during the manufacture of the component.

The production of the component can be done by means of the method according to the invention monitor and thus process quality assurance for carry out the manufactured component. This surveillance can be done for everyone Perform types of resin infusion and resin injection procedures. In particular the procedure can also be carried out if the test object has a Layer structure over fiber fabric layers of the semi-finished fiber product 12 (laminate layers 14), separating film 22, distributor fabric 20 and vacuum film 18.

In Figure 5, the measured depth range is dependent on the Frequency shown in double logarithmic representation. It became one Test specimen prepared, which consists of eight layers of diaxial carbon fiber scrim was put together. It was at a depth of 0 mm, 1 mm, 2 mm, 3 mm and 4 mm each a 10 mm wide film strip arranged. The depth range was determined by which paper tape was recognizable was.

The upper curve is the depth range, which is determined from the phase signature and the lower curve is the one that results from the amplitude signature was determined. One recognizes on the one hand that the depth range at the evaluation via the phase signature is larger.

On the other hand, it can be seen from the diagram in FIG. 5 that at lower ones Frequencies the depth range is higher than at higher frequencies.

Basically, it is the case that the optimal frequency or an optimized Frequency range for the modulation depends on the special component. It however, it can be provided that a calibration test specimen is produced, which is basically the same as the component and also on the infiltrated with resin in the same way. There are certain in the calibration device under test excellent areas generated, for example, via film strips. The frequency is determined so that a desired depth range is detected becomes. The component to be manufactured can then be produced with the frequency determined in this way check during manufacture.

In principle, it is also possible that the frequency when checking the Manufacturing of the component is varied. This can serve, for example, to set an optimized frequency or an optimized frequency range. If suitable frequencies for certain areas (e.g. near the surface or depth ranges) are already known, then a Variation of the frequencies during the check also a variation of the checked areas in particular with regard to their depth relative to the surface be performed. For example, alternating with a smaller and examined at a larger frequency. This also allows (with the higher frequency) near-surface areas and especially the distribution tissue then check for leaks. In particular can be used to check whether there are outgassings or whether air is entering. If a lower frequency is selected, then lower ones can be used Examine areas.

In particular, the speed profile of the resin front is determined by for example, the positions of peaks as a function of time (as in FIGS. 3 (c) and 4 (c) shown). About the determined speed curve irregularities in resin infiltration can be identified.

It is also possible to calculate or estimate the infiltration time. This in turn allows the infiltration process and thus the Automate component production because the end of infiltration can be determined and then automatically, for example, the main feeder can be switched off.

Claims (25)

Process for monitoring the production of a component from a fiber-reinforced material, the component by infiltration of a Semi-finished fiber product is made with liquid resin, during which Infiltration process of the test object with modulated heat waves thermally is excited and the response signal is registered. Method according to claim 1, characterized in that the test object is subjected to heat waves over the entire area. Method according to claim 1 or 2, characterized in that the response signal is determined in reflection. Method according to one of the preceding claims, characterized in that the response signal is determined in transmission. Method according to one of the preceding claims, characterized in that the test specimen is subjected to heat waves in the direction of a distributor fabric. Method according to one of the preceding claims, characterized in that the response signal is registered by a camera. Method according to one of the preceding claims, characterized in that the test specimen is irradiated optically. Method according to one of the preceding claims, characterized in that the heat waves are intensity-modulated. Method according to one of the preceding claims, characterized in that a speed profile of a progressing resin front is determined in the phase signature and amplitude signature. Method according to one of the preceding claims, characterized in that an amplitude signature evaluation is carried out. Method according to one of the preceding claims, characterized in that a phase signature evaluation is carried out. Method according to Claim 10 or 11, characterized in that the amplitude signature and / or the phase signature are determined via Fourier transformation. Method according to one of claims 8 to 12, characterized in that the selected frequency is less than 1 Hz. A method according to claim 13, characterized in that the frequency is less than 0.5 Hz. Method according to one of claims 8 to 14, characterized in that the frequency is greater than 0.0001 Hz. Method according to one of the preceding claims, characterized in that measurements are carried out in a non-stationary temperature state. Method according to one of the preceding claims, characterized in that the test object has a layer structure with layers of semifinished fibers. A method according to claim 17, characterized in that a distribution fabric for the resin is provided, which is arranged on the semi-finished fiber. A method according to claim 17 or 18, characterized in that a vacuum film is provided. Method according to one of the preceding claims, characterized in that the test specimen is thermally excited volumetrically. Method according to one of the preceding claims, characterized in that a defined calibration test specimen is produced and a suitable frequency or a suitable frequency range for the modulation is determined on this. Method according to one of the preceding claims, characterized in that the frequency of the modulation is varied. A method according to claim 22, characterized in that a higher frequency is used to check areas near the surface and a lower frequency is used to check deeper areas. Method according to one of the preceding claims, characterized in that the speed profile of a resin front is determined. Method according to claim 24, characterized in that the production of the component is automated via the determined speed profile.

Images